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Full text of "Practical Organic Chemistry"

QUANTITATIVE  ESTIMATION

the blow-pipe flame is made as hot as possible, but reduced
in length to about 8 to 10 cm. (3 to 4 in,). It is directed at a
point about 2 to 3 cm. (i in.) below the open end to which
the glass rod is attached, the glass rod now serving as a support
whilst the tube is slowly rotated. The glass, if evenly heated
and not drawn out, begins to thicken where the flame plays upon
it, and the inside diameter of the tube contracts. When the
apparent inside diameter of the tube is reduced to about 3 mm.
(i in.), the tube is quickly removed from the flame, and a
capillary end formed by very slowly drawing out the thickened
part of the tube (Fig. 24). When the capillary has so far cooled
as to become rigid, it is sealed off. The tube will now have the

FIG. 23.

FIG. 24.

FIG. 25.

appearance shown in Fig. 25. The tube is kept in a vertical
position until cold. If the tube is of hard glass, a somewhat
different method of sealing is employed. As soon as the glass
is sufficiently soft, it is not thickened, but drawn out at once into
a wide capillary, about ij cm. long. By directing the flame
below this constriction, and continuing to draw out, the capillary
is further lengthened. When it has a length of 2 to 3 cm.
(i in.) it is thickened by revolving it in the flame and then
sealed off. Hard glass is much more easily manipulated in the
oxy-coal gas flame. When cold, the tube is transferred to the
metal cylinder of the-tube furnace. The furnace, conveniently
isolated in case of explosions, should stand on the floor, with
the open end raised and facing a wall. The capillary point



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